Pregnancy Calculators
Free pregnancy calculators. IVF due date, natural due date, conception, ovulation, gestational age, and breastfeeding calorie needs. Science-based tools.
Pregnancy Calculators - Plan and Track Your Pregnancy
Whether you are trying to conceive or already pregnant, accurate date calculations help you plan appointments, understand your fertile window, and track gestational milestones. These calculators use standard obstetric methods (Naegele’s rule, luteal phase dating) referenced by obstetricians and midwives worldwide.
These calculators are for reference and educational planning purposes only - they are not a diagnosis or a substitute for prenatal care. Only a clinical exam and ultrasound can confirm gestational age, fetal viability, and pregnancy health. The clinical risk-scoring tools in this section (VBAC likelihood, VTE risk) illustrate published scoring systems and must never be used to make an actual delivery-mode or anticoagulation decision - those calls belong to your obstetrician, working from your full medical record. If you have any pregnancy symptom that concerns you, contact your healthcare provider directly rather than relying on a calculator.
Dating and Due Date
Fertility and Conception
Clinical Pregnancy Tools
The six dating calculators all rest on the same obstetric conventions but serve different starting points: the Due Date Calculator is the general-purpose entry point from LMP, conception, or ultrasound; the IVF Due Date and Mean Sac Diameter Calculators serve fertility-treatment-specific dating methods that don’t use an LMP at all; and the Reverse Due Date Calculator solves the problem backward, useful after a birth has already happened for record-keeping.
The fertility group covers trying-to-conceive planning end to end: the Ovulation and Clomid Ovulation Calculators predict the fertile window naturally or under a common fertility medication protocol, the Fertility by Age Calculator sets realistic statistical expectations, and the Pregnancy Test Calculator tells you the earliest date a home test can reliably detect a pregnancy based on hCG doubling biology, reducing false-negative frustration from testing too early.
The three clinical tools each illustrate a real obstetric scoring system used in practice - the Breastfeeding Calorie Calculator extends standard BMR/TDEE math with a nursing calorie add-on, the VBAC Calculator reproduces the Flamm-Geiger scoring system for vaginal birth after cesarean likelihood, and the VTE Risk Score Calculator reproduces the RCOG Green-top Guideline 37a scoring system for blood clot risk - both scoring tools are shown for educational reference, since the actual clinical decision requires a clinician working from the complete patient record.
Who Uses These Calculators
People trying to conceive use the ovulation, fertility-by-age, and pregnancy test calculators to time intercourse and testing. Those undergoing fertility treatment use the Clomid and IVF-specific calculators, which follow protocol-specific timelines their fertility clinic will also track. Expecting parents use the due date and gestational age calculators to plan prenatal appointments and understand pregnancy milestones between clinical visits. Nursing and pre-medical students use the VBAC and VTE risk calculators to study real clinical scoring systems - never to make an actual patient-care decision, which always requires a qualified obstetric clinician.
Understanding Conception and Ovulation Timing
Conception occurs when a sperm successfully fertilizes an egg during ovulation. Ovulation typically happens 14 days before the next expected period, regardless of cycle length. Only the follicular phase (LMP to ovulation) varies between women; the luteal phase (ovulation to next period) is consistently 14 days. This is why cycle-length-adjusted due dates differ from the standard 28-day Naegele’s rule: the due date shifts by exactly the number of days your cycle differs from 28.
The fertile window spans 6 days: the 5 days before ovulation and ovulation day itself. Conception rates are highest (25-30% per day) on the two days immediately before ovulation and on ovulation day. Sperm viability of up to 5 days explains why sex earlier in the fertile window can still result in conception.
Frequently Asked Questions
How accurate are LMP-based conception date estimates?
LMP-based dating assumes regular cycles with ovulation on day (cycle length minus 14). For regular cycles, the estimate is accurate within plus or minus 3-5 days. For irregular cycles, an early ultrasound (8-12 weeks) is the gold standard, accurate within plus or minus 5 days. The Conception Calculator adjusts the due date for cycle lengths other than 28 days using the same logic.
What is the difference between gestational age and fetal age?
Gestational age counts from the first day of the LMP and is the measure used by all doctors and ultrasounds. Fetal age (embryonic age) counts from conception, which is typically 2 weeks after LMP. A pregnancy at week 10 gestational age is at week 8 of actual fetal development. Always use gestational age when communicating with healthcare providers.
Can I use the VBAC or VTE risk calculators to decide my own delivery plan or need for blood thinners?
No. The VBAC Calculator and VTE Risk Score Calculator reproduce published clinical scoring systems (Flamm-Geiger and RCOG Green-top Guideline 37a respectively) for educational reference only. Both scores are meant to be one input among many that a clinician weighs against your full medical history, current pregnancy findings, and clinical judgment - they are not designed for patients to self-assess and are not a substitute for your obstetrician's evaluation. Always discuss delivery planning and any blood clot prevention treatment directly with your obstetric care team.